1. Field of the Invention
The present invention relates to methods and apparatus to operate an integrated power tong and back-up tong to make-up and run tubular strings into a drilled borehole.
2. Background of the Related Art
Oil field tubular members, e.g., drill pipe, production tubing and casing, are produced in segments that are coupled with threaded connections at their ends to form tubular strings. It is common to make-up and break-out threaded connections by gripping a first tubular segment and by gripping and rotating an adjacent, second tubular segment relative to the first tubular segment. The two adjacent tubular segments are typically gripped by separate tongs having mechanically, hydraulically or pneumatically-powered jaws that engage the exterior surfaces of the adjacent tubular segments. To achieve relative rotation of the tubular segments to make-up a connection, it is only necessary to rotate one of the two tubular segments using a power tong while holding the other tubular segment generally stationary using a back-up tong. Accordingly, the same two tongs (the power tong and the back-up tong) may be used to make-up or break-out a threaded connection between adjacent tubulars by reversing the rotational direction of the power tong. In this manner, a tubular string may be made-up and extended into the borehole by sequentially connecting and advancing add-on tubular segments, or a tubular string may be tripped out of the borehole by sequentially removing tubular segments from the tubular string.
While it is possible to make-up or break-out a threaded connection by gripping adjacent tubular segments with separate tongs and rotating the body of one or both tongs, this is not common practice due to various safety, spatial and design issues. Rather, common practice includes the use of a power tong having gripping jaws that rotate within the body of the tong. Therefore, the make-up and break-out of a connection can occur without significant swinging motions or significant lateral displacement of either tong.
On a drilling rig, a back-up tong is generally positioned to grip a portion of the tubular string that extends just above the spider, but just below a box end of the uppermost (first) tubular segment that extends through and is grippable by the spider. The power tong is generally positioned above and generally aligned with the back-up tong to grip an adjacent second tubular segment having a downwardly disposed pin end inserted in the box end of the first tubular segment extending through the spider. If the pin end of second tubular segment has been stabbed into the box end of the first segment in preparation to make-up the threaded connection, then the jaws of the power tong are rotated until the connection has been threadably made up. The jaws can be rotated in the direction to “make-up,” or tighten, the connection until reaching a predetermined position or a threshold amount of torque, or a combination thereof. However, if the tubular string is being tripped out of the borehole, then the jaws of the power tong can be rotated in the direction to “break-out,” or unthread, the connection until the uppermost tubular segment of the tubular string is threadably disconnected. It should be clear that the direction of rotation to make-up or break-out a tubular segment depends on whether the threaded connection includes right-handed or left-handed threads.
Reaction forces are forces that result from the application of torque to a tubular segment. For example, if the power tong grips and applies torque to a tubular segment in order to threadably connect the tubular segment to a tubular string that is suspended within a spider, then there will be an equal and opposite torque applied to the power tong. Similarly, as the threaded connection tightens and resistance to further rotation of the tubular segment increases, there will be an increasing amount of torque applied to the suspended tubular string that must be opposed by the back-up tong. In order to secure the back-up tong and power tong against unwanted movement resulting from the reaction forces, it is well-known to secure a snub line between a distal end of each of the tongs and some generally robust structural member of the rig, such as a snubbing post. For example, during a make-up operation involving a suspended tubular string and an adjacent tubular segment, each with standard, right-handed box and pin threads, respectively, the tubular string and the back-up tong that grips the tubular string react and are subjected to clockwise torque applied through the threaded connection by the power tong. Similarly, the power tong is subjected to a force that is equal to and opposite in direction to (counterclockwise) the torque applied to the tubular segment. A snub line to anchor the back-up tong would ordinarily be secured along a line generally tangent to an imaginary circle centered about the axis of the tubular string in order to oppose unwanted rotation of the tubular string or unwanted displacement of the back-up tong. Conversely, the jaws of the power tong bias the adjacent tubular segment to rotate in a clockwise direction to make-up the connection, and a snub line to anchor the power tong would ordinarily be secured to the distal end of the power tong to oppose unwanted displacement of the power tong. While effective, the use of snub lines presents certain hazards and constrains operations and personnel movement on the rig floor, and a solution to this problem has been developed.
An integrated tong system includes a power tong and a back-up tong. An integrated tong system applies, for example, a counterclockwise torque via the back-up tong to oppose a clockwise torque being applied via the power tong by directly coupling the power tong and back-up tong via a structural member referred to generally as a “reaction bar.” The use of a reaction bar to directly react the power tong to the back-up tong generally negates the need to use snub lines and snub posts to provide these reactive forces. Accordingly, an integrated power tong and back-up tong system avoids much of the hazards and constraints of snub lines.
However, an integrated tong system may still cause damage by unwanted displacement of the integrated tong system about the tubular string if the jaws of the back-up tong slip or otherwise lose the grip on the tubular string under the high torque being applied by the power tong to an adjacent tubular segment during make-up or break-out of a threaded connection. If the back-up tong slips under these circumstances, the integrated power tong and back-up tong will begin to rotate counterclockwise about the tubular string. A safety line may be rigged to the system in the same fashion as is used for traditional snub lines to limit tong movement, but the sudden and unexpected motion can lead to damage of equipment.
Accordingly, what is needed is a method and apparatus that avoids damage as resulting from slippage between the tubular string and a back-up tong of an integrated tong system. It would be desirable if one embodiment of the method and apparatus includes minimal adaptation of an existing integrated tong system design.